Vapor generators



June 18, 1957 J, DOWNS 2,796,049

VAPOR GENERATQRS Filed April 6, 1953 INVENTOR John flffiowns BY ATTORNEY VAPOR GENERATORS John N. Downs, Barhertou, Ohio, assignor to The Babcock & Wilcox Company, New York, N. Y., a corporation of New Jersey Application April 6, 1953, Serial No. 347,003

7 Claims. (Cl. 122-32) This invention relates to the construction and operation of vapor generators and particularly to vapor generators utilizing a liquified solid material, such as molten salt, to generate vapor.

There are various commercial processes in which a liquified solid material, such as molten salt, is available at high temperatures as a source of energy which may be used to generate vapor in suitable vapor generating apparatus. In some oil refining processes, for example, liquified salt is used to control the temperature of reactions by acting as a heat absorbing medium. The salt is heated to a high temperature molten state in such processes necessitating the cooling of the molten salt before it can be used again to control the temperature of these oil refining process reactions.

Vapor generating units have been used before to extract heat from these salts, however, in such vapor generating units much difliculty has been encountered in maintaining fluid-tight seals throughout the various pressure parts. The wide variations in temperatures between the molten salt, the vaporizable liquid, the vapor, and the metal parts in contact with these fluids, cause relative thermal expansion and contraction of the pressure parts with resulting strains that may cause failure of the seals between connected parts and leakage throughout the unit. This is aggravated when it is desired to circulate different molten salts simultaneously over different parts of the vapor gen erating surface and particularly when the salts are not at the same temperature. The units heretofore proposed have been supported from the bottom, with the result that pressure parts tending to expand are subject to the weight of the unit and contained fluids which tends to restrict expansion. These units have usually been constructed with heavy flange and bolt connections between pressure parts which add to the weight and strains on [these parts.

The present invention provides a tubular vapor generator especially adapted for the circulation of a high temperature liquified solid, such as molten salt, as a heating medium, and which is characterized by a special construction which permits relative thermal expansion and contraction of the pressure .parts without accompanying strains in the connections between parts which would be likely to result in fluid leakage. My invention also includes a novel construction and arrangement of the pressure parts whereby it is possible to circulate different liquified solids, each at varying temperatures if desired, over difierent portions of the vapor generating surface without straining the parts of the unit due to thermal expansion.

For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred embodiment of my invention.

Of the drawings:

Fig. l is a rear elevation of a steam generating unit constructed in accordance with my invention;

ired States Patent Fig. 2 is a side elevation of the unit shown in Fig. 1;

Fig. 3 is a vertical section taken on the line 3-3 of Fig. 1;

Fig. 4 is a horizontal section taken on the line 4-4 of Fig. 1;

Fig. 5 is an enlarged view of a portion of Fig. 3 illustrating the method of attaching the tube shell and water tube to the steam and water drum; and r Fig. 6 is an enlarged horizontal section taken through one of the salt inlets.

In the steam generating unit illustrated, a horizontally elongated substantially cylindrical steam and water drum is suspended from superja-cent steel work (not shown) by means of encircling straps 11 adjacent the drum ends. The remaining elements, except for the downcomers, are hung from a pair of similar two-part cylindrical drum extensions 12 and 13 which are circumterentially welded at longitudinally spaced points to the bottom of the steam and water drum. The lowermost water-containing space of the unit is defined by two vertically elongated substantially cylindrical water drums 16 and 17 spaced relative to the drum 10 so that their vertical axes are in alignment with the vertical axes of the drum extensions 12 and 13 respectively. Hollow tubular shells 14 and 15 extend between the steam and water drum and the water drums 16 and 17 respectively. Inside each shell are a multiplicity of water tubes 32 having their lower ends expanded into a tube sheet 31 forming the upper end of the corresponding .water drum .and their upper ends expanded into a tube sheet 33 welded to the lower end of the corresponding ex-tension on the steam and Water drum.

As shown in Figs. 3 and 5, the tube sheets 31 and 33 are formed of heavy plate and Welded to the adjacent drum parts. The tube connections to these plates are adequate to support the associated parts and contained fluids from the steam and Water The tube shells 14 and 15 are made in two end to end sections and have their upper and lower ends welded ltO the near sides of the corresponding tube plates 31 and 33. Each tubular shell has a corrugated accordion type expansion joint 21 positioned between and welded to the upper and lower shell sections to permit the shell to expand and contract relative to the enclosed water tubes. Each shell has an inlet 19 at the top and a diametrically opposite outlet 20 at the bottom for the circulation of the molten saltt Molten salt is supplied to the inlet 19 and flows down through the space around the water tubes inside each shell to the outlet 20. The tubes opposite each salt inlet are shielded from erosion by the incoming molten salt by curved metal shields 35. These shields are welded to the tubes and cover the tubes from a level slightly below to a level slightly above the salt inlet openings,

To minimize temperature stresses in and erosion of the tube sheets 31 and 33, protection baflles 34 are arranged to extend horizontally across the tube bundle at a level intermediate the molten salt inlet 19 and outlet 20 and the tube sheets 33 and 31 respectively. The baffles do not have a fluid tight contact with the tubes, so that the spaces adjacent the tube sheets fill with molten salt. The mass of salt remains at substantially a constant temperature regardless of minor temperature variations of the salt entering the inlet 19, causing the corresponding tube sheet to be maintained at a substantially constant temperature. A drain 28 opens to the space ablove the tube sheet 31 to permit removal of the molten sa t.

Each water drum has a flanged bottom section 22 which is bolted on and may be easily removed for inspection of the water drums, tubes and tube sheets 31. A blow-ofii line 29 is connected to the bottom of each water drum. Water is supplied to the unit through feed water connections 23 in one end of the steam and water drum and the generated steam passes oil through the drum outlet 25. A safety valve 26, a vent valve 27 and connections for a gage glass water level indicator 24 complete the fittings of the drum. A manhole cover 39 in one end of the steam and water drum allows access to the internal parts of the drum as well as to the tube sheets 33.

Each water drum is also connected to the steam and water drum by a plurality of external downcomer tubes 18. All of the downcomer tubes have a sinuous configuration to permit expansion and contraction of these tubes relative to the associated pressure parts. As shown in Figs. 1, 2 and 4, the downcomer tubes are arranged in two groups of three tubes each extending from opposite lower portions of the steam and water drum adjacent one end thereof to symmetrically arranged points in the outer half of each water drum. A third set of. six downcomer tubes 18 extends from the lower portion of the drum intermediate the drum extensions 12, 13 with the lower ends of half of these tubes connected to the drum 16 and the other half to drum 17 on the drum sides opposite the downcomers 18.

In assembling the pressure parts, the tubes 32 are first expanded, seal welded and then re-expanded into tube sheet 31. Then the jointed tubular shell is placed over the tubes and welded to the tube sheet. The other tube sheet 33 is attached in a similar manner to the tubes and shell and the whole bundle is then welded to the corresponding extension on the steam and water drum.

In operation one or more molten salts are admitted to the shells 14 and through the inlets 19 and first contacts the shielded tubes. The salt flows into each shell through the spaces surrounding the water tubes 32 giving up its heat thereto in counterflow heat transfer relationship as it flows downwardly to the outlet Ztl. The water in the nests of tubes 32 is heated and vaporized by the salt and the steam generated collects in the steam and water drum it) from which it passes out through the steam outlet 25 to a point of use. The downcomers 18, 18 supply water to the water drums from the water space of the steam and water drum. In the arrangement shown it is possible to circulate a molten heating salt at one temperature through the tube shell 14 and another salt at a different temperature through the other tube shell 15. This is possible because the pressure parts of the unit are suspended freely from the steam and water drum and may expand and contract independently.

Each tube bundle, downcorner tubes, and water drum unit is a compact completely operating section of the complete boiler unit. It is possible with my invention to have a steam drum of any length with as many tube bundles, downcomers and shell assemblies attached to the drum as desired. Thus it is possible to provide a unit employing several kinds of liquid heating material simply by connecting the tube bundles, downcomer tubes and water drums to the size of steam and water drum necessary for the capacity boiler desired and circulating the various heating materials available through diflferent tube shells.

The described construction is characterized by the complete freedom of the parts subject to variation in temperatures to expand and contract without excessive stresses on other parts connected therewith. The described top support arrangement permits the downcomers, tubes, shells, and water drums to hang freely from the main steam and water drum and to expand and contract freely. Using a top support also insures a more stable unit, because the danger of any permanent misalignment to the steam and water drum or connecting parts is overcome by the free expansion of the associated parts. Thus it is unlikely that the steam and water drum would become tilted or misaligned and the danger of a false water level reading with resulting poor steam and water circulation would be eliminated. By using circumferential welds to connect the tube and shell assemblies to an extension piece welded to the steam and water drum, I have eliminated any heavy flange and bolted joints which add to the stress on the lower parts. This method of connecting insures easy assembly of these parts.

While in accordance with the provisions of the statutes I have illustrated and described herein the best form of the invention known to me, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by my claims, and that certain features of my invention may sometimes be used to advantage without a corresponding use of other features.

I claim:

1. Heat exchange apparatus comprising an upper liquid and vapor drum, a lower liquid drum, a shell extending between and structurally connected directly to said drums, tube sheets at the upper and lower ends of said shell, a group of liquid heating tubes within said shell and having their upper and lower ends opening through and connected to corresponding tube sheets, inlet and outlet means near opposite ends of said shell for passing a heating fluid through said shell in contact with said tubes, downcomer tubes externally of said shell and connecting the liquid space of said upper drum to said lower drum, and a tube sheet protection bathe in each of said shells spaced between said inlet means and one of said tube sheets and said outlet means and the other of said tube sheets and arranged to permit a flow of heating fluid to the spaces between said baffies and the corresponding tube sheets.

2. A vapor generator comprising an upper liquid and vapor drum, a plurality of liquid drums, tubular shells connecting said vapor and liquid drum with each of said lower liquid drums, a multiplicity of liquid heating tubes Within each of said shells communicating with the upper liquid and vapor drum and a respective lower liquid drum, a tube sheet at each end of said tubes structurally connected to said tubes and said tube sheets defining a space including said tubes and having heating fluid inlet and outlet openings near opposite ends thereof, and individual metal tube protective shields connected to each of said tubes adjacent said inlet opening.

3. Heat exchange apparatus comprising an upper liquid and vapor drum, a plurality of lower liquid drums, a plurality of shells each extending between one of said lower drums and the upper drum with each shell dependently connected to said upper drum, an expansion joint in each of said shells, tube sheets at the upper and lower ends of each of said shells, a group of liquid heating tubes within each of said shells and having their upper and lower ends opening through and connected to corresponding tube sheets, means for passing a heating fluid through said shells in contact with said tubes, and sinuous shaped downcomer tubes externally of said shells and connecting the liquid space of said upper drum to said lower drums.

4. Heat exchange apparatus comprising an upper liquid and vapor drum, a plurality of lower liquid drums, a plurality of shells each extending between one of said lower drums and the upper drum with each shell dependently connected to said upper drum, an expansion joint in each of said shells, tube sheets at the upper and lower ends of each of said shells, a group of liquid heating tubes within each of said shells, and having their upper and lower ends opening through and connected to corresponding tube sheets, means for passing a heating fluid through said shells in contact with said tubes, and sinuous shaped downcomer tubes externally of said shells and connecting the liquid space of said upper drum to said lower drums, and means for top supporting said drums, tube groups, and shells.

5. Heat exchange apparatus comprising an upper liquid and vapor drum, a plurality of lower liquid drums, a plurality of cylindrical drum extensions welded to the underside of said upper drum, a plurality of tubular shells each extending between one of said drum extensions and one of said liquid drums and dependently connected to said drum extension, an expansion joint in said shell, tube sheets at the upper and lower ends of said shell and welded thereto, a weld connection between said upper tube sheet and said drum extension, a group of liquid heating tubes within said shell and having their upper and lower ends opening through and connected to corresponding tube sheets, means for passing a heating fluid through said shells in contact with said tubes, sinuous shaped downcomer tubes externally of said shell and connecting the liquid space of said upper drum to said lower drums, means for top supporting said drums, tube groups, and shells.

6. Heat exchange apparatus comprising an upper liquid and vapor drum, two lower liquid drums, two shells each extending between one of said lower drums and the upper drum with each shell dependently connected to said upper drum, an expansion joint in each of said shells, tube sheets :at the upper and lower ends of each of said shells, a group of liquid heating tubes within each of said shells and having their upper and lower ends opening through and connected to corresponding tube sheets, means for passing a heating fluid through each of said shells in contact with said tubes, groups of sinuous shaped downcomer tubes externally of said shells and connecting the liquid space of said upper drum at its central portion to each of said lower drums.

7. Heat exchange apparatus comprising an upper liquid and vapor drum, a plurality of lower liquid drums, a plurality of shells each extending between one of said lower drums and the upper drum with each shell dependently connected to said upper drum, tube sheets at the upper and lower ends of each of said shells, a group of liquid heating tubes within each of said shells and having their upper and lower ends opening through and connected to corresponding tube sheets, expansion means for absorbing difierential thermal expansion between said shell and said tubes in each of said shells, means for passing a heating fluid through said shells in contact with said tubes, bent downcomer tubes externally of said shells and connecting the liquid space of said upper drum to said lower drums.

References Cited in the file of this patent UNITED STATES PATENTS 1,757,343 Steinmuller May 6, 1930 1,866,367 Nerad, July 5, 1932 2,197,387 Rowand Apr. 16, 1940 2,220,045 Kraft et a1. Oct. 29, 1940 2,229,554 Cummings Jan. 21, 1941 2,379,661 Sebald July 3, 1945 

